292. Thus it appears that in order to the conclusion that any particular cause must have any particular effect, there is needed first the presence of an impression, and secondly the joint action of those two ‘principles of union among ideas,’ resemblance and contiguity. In virtue of the former principle the given impression calls up the image of a like impression previously experienced, which again in virtue of the latter calls up the image of its usual attendant, and the liveliness of the given impression so communicates itself to the recalled ideas as to constitute belief in their existence. If this is the true account of the matter, the question as to the nature of necessary connexion has answered itself. ‘The necessary connexion betwixt causes and effects is the foundation of our inference from one to the other. The foundation of the inference is the transition arising from the accustomed union. These are therefore the same’. [1] We may thus understand how it is that there seems to be an idea of such connexion to which no impression of the senses, or (to use an equivalent phrase of Hume’s) no ‘quality in objects’ corresponds. If the first presentation of two objects, of which one is cause, the other effect, (_i.e._ of which we afterwards come to consider one the cause, the other the effect) gives no idea of a connexion between them, as it clearly does not, neither can it do so however often repeated. It would not do so, unless the repetition ‘either discovered or produced something new’ in the objects; and it does neither. But it does ‘produce a new impression in the mind.’ After observing a ‘constant conjunction of the objects, and an uninterrupted resemblance of their relations of contiguity and succession, we immediately feel a determination of the mind to pass from one of the objects to its usual attendant, and to conceive it in a stronger light on account of that relation.’ It is of this ‘internal impression,’ this ‘propensity which custom produces,’ that the idea of necessary connexion is the copy. [2] [1] P. 460. [Book I, part III., sec. XIV.] [2] Pp. 457-460. [Book I, part III., sec. XIV.] The transition not to anything beyond sense.